[Boatanchors] Millen 90651 GDO - Fixed

[Richard Knoppow]

----- Original Message ----- 
From: "Ray, W4BYG" <w4byg at att.net>
To: <boatanchors at mailman.qth.net>
Sent: Saturday, January 04, 2014 8:09 AM
Subject: Re: [Boatanchors] Millen 90651 GDO - Fixed


> Glen,
> I also have the mentioned GDO's as well as several others 
> such as B&W, Paco
> and a European Philips tube version.  I use them 
> regularly.
>
> You are a respected and experienced contributor to this 
> and other lists.
> Would you care to expand on your reasoning on your 
> preferred uses for the
> several models?
> 73,
> Ray, W4BYG


     I will add to the list the military AN/APM-10  Some 
sources say this is a military version of the Measurments 
Corp GDO but it isn't, it has a different circuit and 
layout. The Millen is lighter and does the job well. Mine is 
surprisingly accurately calibrated. The Millen will also 
test crystals. You must make an adaptor to connect the 
crystal across the coil jacks.  The capacitor is then 
adjusted for output. The meter will tell you if the crystal 
is oscillating but you need something else to measure the 
frequency.  By interpolation of the GDO tuning scale you can 
determine the optimum capacitance for the crystal. Because 
of the type of circuit the APM-10 won't do this trick, don't 
know about other GDO's.
    I don't have the low-frequency coils for the Millen but 
they look useful.
    One important use for a GDO is tuning up transmitters. 
You can get the plate tuning very close to the correct 
values without powering up the transmitter.  That makes it 
less likely that you will burn up tubes.
    I wonder if Glenn has any reliable information on the 
history of the GDO. AFAIK, they didn't exist before about 
1945, certainly not as commercial items.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com